*** Cellphone Operation in Mountain Regions ***

From: William Laxson <wlaxson@corecom.net>
To: MRA Lister <mra@altadena.net>

...to dissuade
you from relying too heavily on your cell phones in the mountains, I
will share some technical shortcomings of the cellular system as related
to mountain-top use.

1) Digital VS Analog Service

An analog cell site has superior range and is better able to pull in
distant cell phones calling in from mountain top peaks.  Unfortunately,
the current trend is to eliminate analog channels (three times as many
users fit onto the same amount of digital bandwidth).  The day will come
when analog is no longer available.

Digital cell sites measure the distance to the calling phone (an
inherent byproduct of the technology).  Digital cell sites have a
programmable "cut-off" setting to eliminate calls originating beyond a
certain distance.  The cellular operator uses this feature to restrict
the size of the service area so that it doesn't overlap adjacent cell
sites.  Misadjustment of this parameter restricts coverage to distant
mountain top sites.

Do not assume the local cellular carrier knows about and sets this
parameter correctly.  I was stranded on a glacier here in Alaska during
a downed aircraft mission when my helicopter had to make a precautionary
landing (transmission chip detector warnings).  We were looking 20 miles
down glacier right at a major ATT Wireless cell site, full signal
strength, but could not place a call to talk with the helicopter
mechanic.  Later discussions with the ATT Wireless technical director in
our area led to the discovery that their cell sites in the area were
unnecessarily limiting the range beyond the "road system limits".

2) Cell Phones Biased to Use Digital Coverage

Several dual mode cell phones (digital/analog) that I have looked at are
biased toward forcing the user onto a digital service.  This leads to a
situation where a local analog cell site that might provide you with
good service is blocked by a weaker distant digital cell site that will
not provide you service.

When the SEND button is depressed to place a call, the cell phone scans
for all control channel signals and selects the strongest one.  It then
attempts to place a call over that system.

However, in my Nokia phone a weaker digital carrier preempts the
stronger analog one, leading to a case where a call from the mountain
top down to a local analog system never makes it because the cell phone
hears a weak digital control channel from a distant system.

I have learned to force my Nokia 2160 onto the analog channel by placing
the call, which fails, but which leaves the called number in the "last
number dialed" buffer.  I then turn the phone off, then on again.  Just
as the phone completes it's self test, I hit the SEND button.  The call
goes out on the last number dialed and goes over the stronger analog
channel instead of trying to go on the digital channel, perhaps because
it takes longer for the digital channel to be acquired and synched up
during the power up situation.

I offer these examples to make several basic points:

1) The cellular network and cell phones are  designed, maintained, and
optimized for high density use by local area subscribers, not for
distant, weak signal subscribers.  Be happy when your phone works in the
distant mountains but don't expect it to (even if it did last week)!

2) The cellular network system standards are constantly changing,
upgrading, moving to digital delivery of internet content, etc.  In
every market, subscriber density is rapidly climbing, leading to
constant addition of new sites, relocation of old ones, constant fine
tuning of the system channels and parameters.  The frequency bands used
for cellular service delivery are getting higher and higher (the 800 MHz
original system is rapidly being supplanted by the 1900 MHz PCS system,
and even higher frequencies are in the works).  The higher frequencies
do not work as well to distant mountain tops!  

3) The cell phone designs are constantly changing, and their intrinsic
operation is driven by the large nation wide carriers (ATT Wireless for
example) who fine tune phone operation to meet system needs (put more
people onto their systems).   

Have you wondered why the carriers offer you a replacement phone
for $5.00 if you will just subscribe to their latest and greatest plan
for a year?  It's partially to slow down churn, but also to eliminate
the older
technology that uses their system less efficiently.

Your new phone may not work as well from the mountain top next year! 
Your existing one may not either.

William Laxson
Alaska Mountain Rescue Group
MRA Communications Committee Chair
wlaxson@corecom.net